1. Technical Field
This invention relates to solar battery modules of portable or other types as typified by electronic equipment applications having solar batteries built therein, and more particularly, to solar battery modules serving as photovoltaic devices which when integrated in equipment, provide a harmony of color, and especially of design and have a color not causing an odd sensation despite solar battery mounting.
2. Background Art
Solar batteries are utilized in various electronic equipment as a power supply substitute for dry batteries. In particular, low power consumption electronic equipment such as electronic desktop calculators, watches, and portable electronic equipment (e.g., cameras, cellular phones and commercial radar detectors) can be fully driven by the electromotive force of solar batteries, so that the equipment can operate semi-permanently without a need for battery replacement. Because of the semi-permanent operation combined with cleanness to the environment, solar batteries are of great interest.
When solar batteries are built in electronic equipment, a consideration must be taken from the design aspect. In particular, modern electronic equipment are at an equal performance level imposing difficulty to discriminate one as superior in performance to another and the choice of a product by the consumer often depends on the superiority of design. Because of the structure of the solar battery, the mechanism of the light-receiving surface is visually perceivable from the exterior. Therefore, the design is largely affected by the difference in brightness or color between the photoelectric conversion section having a photoelectric converting function on the light-receiving surface and other regions such as electrodes, isolation walls and other structures. As a general rule, if these structures are viewed from the exterior, most of them have a detrimental effect on the design.
JP-A 60-148174 discloses a solar battery comprising at its front face a selective reflecting layer (multilayer interference filter such as a dichroic mirror) which selectively reflects a portion of visible light having a specific wavelength band, transmits the reminder and transmits at least a portion of light in a wavelength band contributing to the power generation of the solar battery and a light diffusing layer disposed on the front surface of the selective reflecting layer. With this construction, the solar battery exhibiting a dark color becomes the lowermost layer, the xe2x80x9cselective reflecting layerxe2x80x9d is provided as an upper layer on its light-receiving surface side for changing the color to a color of preference, and a xe2x80x9cdiffuse transmission layerxe2x80x9d is provided as an upper layer thereon for rendering the reflected light brighter for reducing the dark color of the solar battery so that the color is controllable to some extent. This allows for a freedom of design of the color and other factors of the built-in system, thereby mitigating the odd sensation in product design caused by incorporating the solar battery.
The solar battery module that has been used in practice has a photoelectric conversion film capable of producing a photovoltaic force, a transparent electrode, a comb-shaped collector electrode in the form of a conductive silver film formed on the transparent electrode, and a conductive film of Ag, Cu, Ni, Mo or alloys thereof, carbon black or graphitized carbon black serving as a peripheral wiring electrode. The transparent conductive films known in the art include SiO2-doped ITO films, SnO2 films inclusive of Sb or F doping type), and ZnO films (inclusive of In, Al or Si doping type). Of these, ITO is commonly used. In addition, by forming a multi-stage cell structure capable of producing a desired high voltage on a single substrate, by forming a printed insulating film for patterning necessary for series connection, by effecting laser scribing/patterning by a dry process followed by printing of an insulating resin thereon to form barriers, or by printing conductive ink to form a laser bonding structure, an integrated structure is established (this is more outstanding in the case of a film solar cell which is easy to form into an integrated structure). With respect to the color of the solar battery as viewed from its light-receiving surface, a uniform color surface given by the interference color of the transparent electrode thin film (dictating the majority of the color of the solar battery) which is overlapped by the color of the xcex1-Si photoelectric conversion film is mixed with patterns of various line widths having optical characteristics including high light reflectance, high light absorbance, high light transmittance and specific wavelength absorption caused by the formation of the above integrated structure, interfering with the color harmony from the design standpoint.
One patterning process is capable of integrating a transparent electrode formed on a substrate by sputtering through a metal mask, a photoelectric conversion film by plasma CVD, and a metal electrode by sputtering together, without using screen printing or laser scribing. Of these components, the metal electrode overlapping the mask shielding area exhibits a high reflectance and provides a high contrast to the photoelectric conversion section within the non-mask shielding area, giving an odd sensation. It is quite difficult to eliminate the odd sensation even when a diffuse transmission layer is formed on top of the cell to provide a shield.
Accordingly, even when the selective reflecting layer and diffuse transmission layer described in the above-referred patent are formed as upper layers on the light-receiving surface side of the solar battery, various pattern lines which are different in brightness, color, reflectance and clearness due to the respective optical characteristics are viewed as being admixed in the uniform color surface and look like a relief. To render these pattern lines to be not perceivable to the view is a key factor in eliminating the odd sensation in product design caused by building in the solar battery although the conventional solar battery design lacked a careful consideration taken to allow for a freedom of product design. In particular, for the xe2x80x9csolar watchxe2x80x9d in which the movement can be driven by the electromotive force that a solar battery produces at an indoor low illuminance, stringent design requirements are imposed. Further, when a watch dial plate of a color selected from a wide range, though frequently white, serving as a selective reflecting layer and a diffuse transmission layer too is provided as an upper layer on the light-receiving surface side of the solar battery, the gap therebetween should be reduced to a nearly contact state due to the thickness reduction demand. The above requirements should be met even under such service circumstances.
Further, the solar battery module is required to improve the power generation efficiency at a given light source and illuminance, or to form a multi-stage integrated structure to improve the voltage to comply with the requirement of a particular device used, to thereby improve battery performance whereas giving the solar battery-built-in product itself a freedom of design in harmony with the surrounding environment is also a technical task to be solved for the solar battery to find a wider range of market as a clean energy source.
An object of the invention is to provide a solar battery module having a high efficiency power generating capability, maintaining a design harmony, free of an odd sensation, having a freedom of design, stable to changes in the environment such as outdoor or indoor temperature and humidity, and having a high dimensional precision.
In the solar battery module of the invention, an insulating ink having a hiding power and a color closest to the color of the solar battery surface (almost dictated by the interference colors of an ITO transparent electrode thin film) is prepared, and an insulating pattern and electrode exposed on the solar battery surface are concealed by patterning the ink of this color by a screen printing technique. With respect to an insulating pattern and conductive pattern having a different color from the solar battery surface, having a high light reflectance, high light absorbance, high light transmittance, and specific wavelength band absorption and exposed to the solar battery surface, the same ink is overcoated by a similar printing technique to a minimum thickness necessary to maintain hiding. This unifies the solar battery surface to a uniform color. Although a contrast is ascertainable with a pigment-dispersed ink film having a higher content of diffuse reflectance components unlike a high reflectance film formed by a dry process, the contrast is mitigated, maintaining a color harmony in design.
To obtain a solar batter cell whose solar battery surface is unified to a uniform color, which becomes the lowermost layer and in which a xe2x80x9cdiffuse transmission layerxe2x80x9d is provided as an upper layer on its light-receiving surface side or to obtain a solar battery of any desired color, the cell in which the diffuse transmission layer itself is given a color or the xe2x80x9cselective reflecting layerxe2x80x9d is provided as an upper layer on the xe2x80x9cdiffuse transmission layerxe2x80x9d or as an intermediate layer between it and the solar battery is effective.
The above and other objects are achieved by the following constructions.
(1) A solar battery module comprising, on a light-receiving surface thereof,
a photoelectric conversion section for converting incident light into electricity, said photoelectric conversion section comprising silicon, and
an insulating color film disposed in regions other than said photoelectric conversion section for reducing a color difference from said photoelectric conversion section.
(2) The solar battery module of (1) wherein said insulating color film comprises pigment particles dispersed in a binder.
(3) The solar battery module of (1) wherein said insulating color film comprises a microparticulate white pigment as pigment particles dispersed therein.
(4) The solar battery module of (1) wherein said photoelectric conversion section comprises a non-single-crystal silicon film.
(5) The solar battery module of (1) further comprising a diffuse transmission layer above the light-receiving surface of the solar battery module.
(6) The solar battery module of (5) wherein the color difference xcex94E between the insulating color film and the photoelectric conversion section as perceived through the diffuse transmission layer is up to 5.0.
(7) The solar battery module of (5) further comprising a selective reflecting layer above and/or below said diffuse transmission layer.
(8) The solar battery module of (5) wherein said diffuse transmission layer has an overall light transmittance of at least 20% and a haze of at least 8% in the visible spectrum.
(9) The solar battery module of (1) wherein said photoelectric conversion section has a transparent conductive film.
(10) The solar battery module of (1) comprising a substrate made of any of light transmissive, heat resistant resins, glass and stainless steel.
(11) The solar battery module of (1) wherein a hot-melt web having a buffer adhesive layer containing a thermosetting resin is laminated on at least one surface of a substrate made of any of light transmissive, heat resistant resins, glass and stainless steel.
(12) The solar battery module of (11) wherein said substrate and/or said buffer adhesive layer contains a UV absorber or has a UV absorber localized on a surface thereof.
(13) The solar battery module of (11) wherein said buffer adhesive layer contains an organic peroxide.
(14) The solar battery module of (11) wherein the hot-melt web has a support film, and the support has a glass transition temperature of at least 65xc2x0 C. or a heat resistant temperature of at least 80xc2x0 C. prior to thermocompression bonding.
(15) The solar battery module of (11) wherein the hot-melt web has a support film, and the support has a molecular orientation ratio (MOR) of from 1.0 to 3.0 prior to thermocompression bonding.
(16) The solar battery module of (11) wherein the organic peroxide has a decomposition temperature of at least 70xc2x0 C. at a half life of 10 hours prior to thermocompression bonding.
(17) The solar battery module of (1) further comprising a protective coating film having light transparency and heat resistance on said photoelectric conversion section.
(18) A solar battery module further comprising a layer of the hot-melt web of (11) on said protective coating film.
(19) A watch comprising the solar battery module of (1).
In the prior art solar battery, no consideration has been made on the unification of color including colored portions of fine wires constructing various functional patterns indispensable for battery formation other than the color of a power generating layer, that is, a photoelectric conversion section. Therefore, an approach of forming a selective reflecting layer and a diffuse transmission layer having both functions of diffusing and transmitting incident light as upper layers on the light-receiving surface while insuring a power generating capability failed to achieve hiding by unifying colors including the colored portions of the respective functional patterns other than the color of the photoelectric conversion section. According to the invention, an insulating ink having a color closest to the color of the photoelectric conversion section is prepared and as such, used to form an insulating pattern film on the surface-exposed portions of the solar battery. Alternatively, with respect to an insulating pattern and conductive pattern having a high light reflectance, high light absorbance, high light transmittance, and specific wavelength band absorption, an ink hiding process of overcoating them with the same ink as an upper layer is effective.
To obtain a solar battery of whitish or light surface color and of high quality, a method of using as the lowermost layer the cell in which the surface of the solar batter has been unified to a uniform color by the above-mentioned ink hiding process, providing a diffuse transmission layer as an upper layer on its light-receiving surface side, and further providing a selective reflecting layer is quite effective.
As expressed by the L*a*b* color space (representing brightness, redness and blueness, respectively), the color difference value xcex94E between the photoelectric conversion section and the regions other than the photoelectric conversion section coated with the insulating color ink is 3.0 or less. Also, the color difference value xcex94E between the surface color of the solar battery as perceived through the diffuse transmission layer (based on a white filter) and the color of the insulating color ink approximate to the surface color of the solar battery as perceived through the diffuse transmission layer (based on a white filter) is preferably up to 3.0, more preferably up to 2.0. In this case, the values of the L*a*b* color space of the surface color of the solar battery as a reference are (44.51, 6.47, 2.24), respectively, whereas the values of the L*a*b* color space of the surface color of the while filter (diffuse transmission layer) used are (69.12, 0.93, 3.88), respectively. The white filter has an overall light transmittance Tt of 47.9%, a diffuse transmittance Td of 33.8%, and a haze value of 70.6%.
For solar watches using ordinary whitish dial plates, the most effective insulating color ink approximate to the surface color of the solar battery is a current insulating ink whose pigment component is a mixture of rutile type titanium dioxide having a high hiding power and a brown pigment (e.g., red iron oxide) having light resistance.
As to watches for outdoor use such as sports diver watches, on the other hand, solar watches of a design having a blackish dial plate are popular. In this case, filters having a low brightness such as blackish filters having an overall light transmittance of 40 to 20% in the visible spectrum, a haze value of 10 to 15% indicating a diffuse transmittance of substantially nil, and a brightness L* as low as about 10 are often used as the diffuse transmission layer. When such a filter is provided on the light-receiving surface side, the tone of this filter itself is visually seen more blackish than the tone of the solar battery surface color as visually seen through the filter. As a consequence, the measure of unifying the battery surface color as required on the use of the above whitish filter having a high overall light transmittance and diffuse light transmittance is not needed. It creates least odd sensation on visual observation that the tone of the hiding ink to be overcoated as an upper layer on the non-power generating regions of the solar battery is made closer to the tone of reflected light which is reflected by the photoelectric conversion film of the cell through a blackish, low-brightness filter and visually seen substantially black. In this case, even if the color difference xcex94E between the power generating film and the ink is considerably in excess of 3.0, by virtue of the black tone and extremely low transmittance of the black dial plate (the dial plate used in a typical example had a Tt of 2.6%, a Td of 2.7% and a haze of 10.7%) and the substantial elimination of light diffusing effect, the tone of return light which is reflected by the cell surface and visually seen through the filter (black dial plate) largely depends on the optical characteristics of the filter (black dial plate) only when the black filter is used. The watch is visually seen to have a unified black tone substantially independent of the magnitude of the color difference between different regions within the cell, as long as high reflectance metallic luster regions are partially absent.